fix(@angular/build): address review feedback in sourcemap ignore-list plugin

Address review comments for the fast sourcemap ignore-list implementation:
- Only bypass the fast path when IGNORE_LIST_BYTES is present in the buffer instead of skipping the file completely, preventing false positives if the token appears in sourcesContent.
- Check if the ignore-list extension property already exists on the parsed map object in the fallback slow path to avoid duplicate insertion.
- Validate that every element in the extracted sources array is a string to prevent runtime errors.

Author: alan-agius4

packages/angular/build/src/tools/esbuild/sourcemap-ignorelist-plugin.ts

@@ -85,7 +85,9 @@ function extractSources(contents: Buffer): string[] | undefined {
           const slice = contents.toString('utf-8', arrayStartIndex, i + 1);
           const parsed = JSON.parse(slice);
 
-          return Array.isArray(parsed) ? (parsed as string[]) : undefined;
+          return Array.isArray(parsed) && parsed.every((s) => typeof s === 'string')
+            ? (parsed as string[])
+            : undefined;
         } catch {
           return undefined;
         }
@@ -153,34 +155,40 @@ export function createSourcemapIgnorelistPlugin(): Plugin {
             continue;
           }
 
-          // If the ignore list is already present, avoid duplicate insertion
-          if (contents.includes(IGNORE_LIST_BYTES)) {
-            continue;
-          }
+          let fastPathSuccess = false;
+          if (!contents.includes(IGNORE_LIST_BYTES)) {
+            const sources = extractSources(contents);
+            if (sources) {
+              const ignoreList: number[] = [];
+              for (let index = 0; index < sources.length; ++index) {
+                const location = sources[index].indexOf('node_modules/');
+                if (location === 0 || (location > 0 && sources[index][location - 1] === '/')) {
+                  ignoreList.push(index);
+                }
+              }
 
-          const sources = extractSources(contents);
-          if (sources) {
-            const ignoreList: number[] = [];
-            for (let index = 0; index < sources.length; ++index) {
-              const location = sources[index].indexOf('node_modules/');
-              if (location === 0 || (location > 0 && sources[index][location - 1] === '/')) {
-                ignoreList.push(index);
+              if (ignoreList.length === 0) {
+                continue;
               }
-            }
 
-            if (ignoreList.length === 0) {
-              continue;
+              const updated = updateSourcemapFast(contents, ignoreList);
+              if (updated) {
+                file.contents = updated;
+                fastPathSuccess = true;
+              }
             }
+          }
 
-            const updated = updateSourcemapFast(contents, ignoreList);
-            if (updated) {
-              file.contents = updated;
-              continue;
-            }
+          if (fastPathSuccess) {
+            continue;
           }
 
           // Fallback to full JSON parse/stringify if fast scanning or splicing fails
           const map = JSON.parse(contents.toString('utf-8')) as SourceMap;
+          if (map[IGNORE_LIST_ID]) {
+            continue;
+          }
+
           const ignoreList = [];
 
           // Check and store the index of each source originating from a node modules directory